The present invention is directed to a system and method for removing contaminants from a liquid, and more particularly, concerns a system and method for removing contaminants from wastewater.
Modern federal, state and local water standards, waste disposal guidelines as well as environmental concerns have forced many manufacturing or processing businesses which produce wastewater or process effluents which do not meet the new standards to either shutdown, pay large penalties or surcharges, or implement expensive wastewater treatment equipment. Although it is not particularly difficult to remove relatively large wastewater contaminants such as screenable or large settleable solids, it is extremely difficult to remove suspended solids (total suspended solids TSS), biological organic discharge or biochemical oxygen demand (BOD), fats, oils and greases (FOG), chemicals, metals, salts, certain organic compounds, toxic materials, bacteria, colloidal materials, soluble materials, and chemically bound molecular substances. If a business does not implement a system for treating their contaminated wastewater before disposing of it in the municipal sewer system, they are subject to large monetary surcharges or fines which serve to reimburse local sewage treatment facilities for having to treat the contaminated wastewater.
As an example, a modern meat rendering facility for grinding and processing a variety of meat products for pet food utilizes an abundant supply of water during the meat rendering process and for cleaning the meat products, processing equipment, and plant facilities. The raw wastewater produced by such a rendering facility includes contaminants such as blood, grease, bone, meat, metal, fats, oils, dirt, grit, and the like. Such rendering process wastewater may contain 2,000-8,000 mg/l BOD, 800-4,000 mg/l TSS and over 4,000 mg/1 oil and grease. In order to avoid having to pay a tremendous surcharge in order to dump such raw wastewater into a municipal sewer, the wastewater must be treated to significantly reduce the BOD, TSS and oil and grease content.
Water treatment systems for reducing the contaminant levels of raw wastewater to meet modern standards and to be acceptable for either direct disposal in a septic system, recycling through the industrial process or disposal in a municipal sewer system without a penalty or surcharge, is either nonexistent or is so outrageously expensive that most businesses end up paying the surcharges or fines for dumping the raw wastewater into the municipal sewer or paying large fees for storage and disposal thereof. Direct disposal of the raw wastewater costs the company not only the exorbitant surcharges or disposal costs, but also costs the company the benefit of recycling certain valuable components of the wastewater or process effluent.
Conventional static screens ranging from bar screens having large openings of up to two inches to round hole or square mesh screens having very small openings down to 0.01 of an inch may be used to remove large solids and surface debris from wastewater or process effluents. However, static screens tend to clog easily resulting in blinding of the screen and require frequent maintenance. Also, static screens do not reduce the BOD, FOG or TSS contaminants sufficiently to avoid the payment of surcharges.
Externally or internally fed rotary drum strainers provide better wastewater treatment than static filters by improving product recovery, liquid recovery, removal of solid sludges and surface debris sized larger than the openings in the strainer, and reducing sewage requirements and surcharges. However, rotary drum strainers do not eliminate sewage requirements and surcharges by substantially reducing BOD, FOG, and TSS contaminants and also may be prohibitively expensive when faced with wastewater flow rates of over 50,000 gallons per day.
Conventional drain and grease traps including wetting agents for penetrating crusted grease and organic material to break it apart and bacteria to eat and digest the grease, fats, oils and other organic material may be effective at treating low flow rates of relatively clean wastewater, but are impractical and cost prohibitive at treating highly contaminated wastewater at flow rates of over 2,000 gallons per day.
Further, reverse osmosis, nanofiltration, ultrafiltration and microfiltration units including spiral, tubular, ceramic, hollow fiber, and plate and frame membrane configurations may be effective at removing some contaminants from waste effluents or wastewater and at reducing BOD, but may not eliminate sewage surcharges and tend to be very expensive. For example, an estimated budget of $400,000 was considered for a filtration unit which could treat 421,000 gallons per month of poultry processing plant wastewater.
Also, conventional technology in water treatment systems and filtration units may require the use and expense of a combination of different types of treatment units for treating heavily contaminated wastewater. For example, a combination system may include a large sized static screen and a rotating drum filter unit upstream of a reverse osmosis membrane filter so as to reduce clogging and avoid damage to the membrane filter.
Hence, there is a need for an improved wastewater treatment system which can handle heavily contaminated effluents such as meat rendering plant wastewater, which can handle wastewater flow rates of 50,000 or more gallons per day, which is relatively inexpensive to construct and easy to maintain and operate, and which can reduce the BOD, TSS and FOG contaminant levels down to acceptable, permitted levels.